The present invention is directed to a method for the automatic adjustment of a switch means for automatically switching between a reception operating mode and a transmission operating mode in a hands-free means of a communication terminal equipment. DE 44 47 028 A1, for example, discloses such a method.
In DE 44 47 028 A1, there is disclosed a reception signal branch in which received signals are processed and output via a loudspeaker, a transmission signal branch in which signals received via a microphone are processed and output, and adjustable switch means by which attenuation stages provided in the reception signal branch and the transmission signal branch can be selectively driven dependent on signals transmitted via the reception signal branch and the transmission signal branch and whose sensitivity for the signals transmitted via the reception signal branch and the transmission signal branch can be set upon employment of an audio signal generator.
The hands-free means to be adjusted with the method described in DE 44 47 028 A1 is a component part of a digital communication terminal equipment such as, for example, a telephone or the like, and comprises a reception signal branch, a transmission branch and a switch means for automatically switching between a reception operating mode and a transmission operating mode.
The reception signal branch serves the purpose of processing input signals received via an input terminal and outputting them via a loudspeaker; the transmission signal branch serves the purpose of processing input signals received via a microphone and outputting them via an output terminal.
In the reception operating mode, signals received from the input terminal are output via the loudspeaker, while the forwarding of signals received via the microphone to the output terminal is entirely or partially suppressed; in the transmission operating mode, signals received via the microphone are forwarded to the output terminal, while the output of received signals from the loudspeaker is entirely or partially suppressed.
The "normal" operation of one of the reception signal branch or the transmission signal branch and the inhibit (attenuation, interruption) of the other branch particularly serves the purpose of avoiding a coupling of signals from the reception signal branch onto the transmission signal branch. Such a coupling of signals from the reception signal branch onto the transmission signal branch is usually caused by signals output by the loudspeaker of the reception signal branch being picked up by the microphone of the transmission signal branch. This effect, of course, is undesirable si nce the signals to be actually transmitted are thereby provided with an echo or are overlaid by a feedback whine.
For selective activation of either the reception signal branch or of the transmission signal branch and for inhibiting the nonactivated branch, the apparatus disclosed in DE 44 47 028 A1 includes an attenuation unit in its reception signal branch and its transmission signal branch, these being selectively driveable by the switch means.
The switch means drives the attenuation stages according to the signals conducted over the reception signal branch and the transmission signal branch. A voice signal comparator is utilized with which the levels of the respective signals are compared. In order to lend the voice signal comparator different sensitivities for the signals to be compared, it being particularly significant for handling what is referred to as the reception-side self-interruption, an amplifier with variable gain factor precedes one of the inputs of the voice signal comparator. The switch behavior of the switch means can be influenced by setting the gain factor of this amplifier.
The determination of the optimum setting of the gain factor ensues upon employment of an audio signal generator with which an audio signal is supplied into the reception signal branch as a reception signal (pseudo voice signal) during the adjustment process. The gain factor of the amplifier is adjusted for determining the optimum setting thereof until the point is reached at which the switch means initiates a switching from the reception operating mode into the transmission operating mode. Proceeding from this setting, the gain factor is again modified at the end of the process to a certain extent so that the hands-free means is sure to retain its readiness to receive, i.e. that switch events that disturb (interrupt) the intended communication are avoided.
Even when it is automatically implemented, such a setting of the gain factor is relatively time-consuming and, above all, inexact because the gain factor which is recognizable in the described way can be respectively approximately set to the respectively optimum value. A non-optimum selection of the gain factor results in that the switching between the operating modes of the hands-free means does not ensue at the proper times, i.e. too early, too late or not at all, as a result whereof communication via the hands-free means is substantially deteriorated under certain circumstances or even rendered impossible.